Pre-warm find_all_candidates cache in finder

src/pip/_internal/resolution/resolvelib/resolver.py

@@ -1,7 +1,7 @@
 import functools
 import logging
 import os
-from typing import TYPE_CHECKING, Dict, List, Optional, Set, Tuple, cast
+from typing import TYPE_CHECKING, Dict, Iterator, List, Optional, Set, Tuple, cast
 
 from pip._vendor.packaging.utils import canonicalize_name
 from pip._vendor.resolvelib import BaseReporter, ResolutionImpossible
@@ -19,6 +19,7 @@
     PipDebuggingReporter,
     PipReporter,
 )
+from pip._internal.utils.parallel import LACK_SEM_OPEN, map_multithread
 
 from .base import Candidate, Requirement
 from .factory import Factory
@@ -66,6 +67,7 @@ def __init__(
         self.ignore_dependencies = ignore_dependencies
         self.upgrade_strategy = upgrade_strategy
         self._result: Optional[Result] = None
+        self._finder = finder
 
     def resolve(
         self, root_reqs: List[InstallRequirement], check_supported_wheels: bool
@@ -87,6 +89,8 @@ def resolve(
             reporter,
         )
 
+        self.prime_finder_cache(provider.identify(r) for r in collected.requirements)
+
         try:
             try_to_avoid_resolution_too_deep = 2000000
             result = self._result = resolver.resolve(
@@ -161,6 +165,22 @@ def resolve(
         self.factory.preparer.prepare_linked_requirements_more(reqs)
         return req_set
 
+    def prime_finder_cache(self, project_names: Iterator[str]) -> None:
+        if LACK_SEM_OPEN:
+            return
+
+        if not hasattr(self._finder.find_all_candidates, "cache_info"):
+            return
+
+        def _maybe_find_candidates(project_name: str) -> None:
+            try:
+                self._finder.find_all_candidates(project_name)
+            except AttributeError:
+                pass
+
+        for _ in map_multithread(_maybe_find_candidates, project_names):
+            pass
+
     def get_installation_order(
         self, req_set: RequirementSet
     ) -> List[InstallRequirement]:

tests/unit/test_finder.py

@@ -558,3 +558,23 @@ def test_find_all_candidates_find_links_and_index(data: TestData) -> None:
     versions = finder.find_all_candidates("simple")
     # first the find-links versions then the page versions
     assert [str(v.version) for v in versions] == ["3.0", "2.0", "1.0", "1.0"]
+
+def test_finder_caching(data: TestData) -> None:
+    finder = make_test_finder(
+        find_links=[data.find_links],
+        index_urls=[data.index_url("simple")],
+    )
+    def get_findall_cacheinfo():
+        cacheinfo = finder.find_all_candidates.cache_info()
+        return {k: getattr(cacheinfo, k) for k in ['currsize', 'hits', 'misses']}
+
+    # empty before any calls
+    assert get_findall_cacheinfo() == {"currsize": 0, "hits": 0, "misses": 0}
+
+    # first findall is a miss
+    finder.find_all_candidates("simple")
+    assert get_findall_cacheinfo() == {"currsize": 1, "hits": 0, "misses": 1}
+
+    # find best following a find all is a hit
+    finder.find_best_candidate("simple")
+    assert get_findall_cacheinfo() == {"currsize": 1, "hits": 1, "misses": 1}